In an election year people tend to stock up. This year there are, according to news reports, many new gun buyers adding to ammo sales. When President PHRASECENSOREDPOSTERSHOULDKNOWBETTER. won in his first term gun sales increased, on the assumption that he would promote anti-gun policies. For the most part this didn't happen, but gun owners are a nervous lot.

Edited to add - I post this as a straight forward answer to the question, without political comment.